The presence of pathogenic cells in the bloodstream or the spread of pathogenic cells from other sites to the bloodstream is one of the important factors that determines whether or not a diseased patient will survive. For example, the spread of malignant cells from the primary neoplasm to distant organs is an important factor in determining whether cancer patients will survive. Likewise, the spread of microorganisms to the bloodstream is important in determining whether a patient with an infection will survive. Highly sensitive methods must be developed that can detect and quantitate circulating pathogenic cells, such as metastatic cells, microorganisms, and other types of pathogenic cells in the vasculature at the earliest stages of disease. Achievement of this objective requires probes with selectivity for the pathogenic cells, biocompatibility, and the ability to perform deep tissue imaging.
Flow cytometry is a method that is used for characterizing and quantitating target cell populations using fluorescent probes that render high specificity and low background measurements. However, flow cytometry requires repeated acquisition of samples for examination. Accordingly, the use of this technique for examining the blood of patients is discouraged because of the invasive nature of the sampling that is required. Furthermore, traditional flow cytometry cannot be used for real-time analysis in vivo. Also, the delay between sampling and analysis of the samples may change the host environment so as to cause artificial changes in the samples.
More recently, a conceptual in vivo flow cytometry technique utilizing confocal microscopy has been described for the real-time detection and quantitation of flowing tumor cells in vivo (Georgakoudi, et al. (2004) Cancer Res., 64, 5044-5047; Novak, et al. (2004) Optics Lett., 29, 77-79). However, there is no available method with the requisite sensitivity, biocompatibility, and ability to perform deep tissue imaging for performing the noninvasive detection and quantitation of pathogenic cells in vivo using techniques to label the pathogenic cells in the bloodstream.